Beedy is quite correct. And the people who believe in heirship by physical descent are not so ignorant as to have missed this. Of those who treat heirs of God's promise as physical descendants of Abraham, I do not think that anyone includes the physical descendants of Ishmael. Nor, for that matter, do I think that anyone includes the physical descendants of Esau. I think they all trace heirship exclusively by Isaac to Israel (Jacob), and then to all physical descendants in succeeding generations. I spoke of Abraham because Paul did so in Romans. But the points made by Paul (and me) are the same whether we start with Abraham or with Isaac or with Jacob/Israel.